I've seen Ben VDS lots of time on my favourite spot in Holland.
Believe me, he's always on sails 1 - 2 m2 bigger as I am.
Typically when I'm on my 6.7, he's on his 8.6.
That's why he's a pro and I'm an amateur

On the Isonics I only use race sails.
And I agree with Ken, it's nice to have a big choice although life could be simpler.
To make this complicated choice much easier, I use an anemometer.
Winds change.Tell me something new. That's why I postpone the sail choice as long as possible. Logical, not ?

About throwing money at the sport.
At the moment I don't have any board nor sail that I've bought new. All 2nd hand.
But it's still expensive enough.

It will be great if US and UK use the metric system like the rest of the world. However, human beings are reluctant to change. We are creatures of habits. If one grew up in an environment where imperial units were used, then metric will appear strange and vice versa. The older a person, the more difficult it is to change. Just getting the windsurfers of the world to use the same unit of measurement is impossible!

The great thing about the Beaufort Scale is that it is independent of the unit of measurement because the same wind force can be converted to m/h, m/s, km/h or knots.

(It is interesting to note that not all things nautical are measured in knots. F1 powerboats are measured in km/h or m/h.)

I find it interesting that those that should know, frequently assume that mankind is not capable of changing/learning through immersion. We all can adapt very quickly if there is only one option.

In the US, especially Texas where the state and public school systems are confronted with a HUGE influx of non English speaking aliens. The schools almost all choose bi-lingual education (with poor results), rather than full immersion in English. You think educators would be smarter. Actually, the teachers are smarter, but it's the state and local governments that are not.

I still believe that it is politics that is driving this boat not results, same with the metric system.

I was out yesterday in Beaufort 3.5 with my formula board and 11.0 and hit a top speed of 23 knots.

One reason why I prefer knots to Beaufort scale is the broad range covered by F4. At 11 knots I might be hardly planning with 7.8 mē - my biggest sail - while in consistent 15 knots plus gusts I may be happy with 6 mē and a small board. It is not the case in F5 or F6 where a single sail/board combo is more likely to cover the whole range. Of course I will pick one size that suits the average wind of the day, but F4 means virtually nothing although it is the sweetspot of many sailors.

Today was typical "F4" weather. Forecast was 12 knots in the morning and 15 in the afternoon. Indeed when I arrived the wind was still moderate so I rigged my Naish GP 7.8 on the Falcon 112 and here we go. At some point the wind started to increase and I thought: well it's F4 rignt? Let's give a bit more outhaul to the sail. And just when everything was perfectly balanced... my wishbone broke!! Floating back to the shore I noticed a few guys much heavier than me with sub seven sails (admittedly they were not planing all the time). Then I rigged my Sprint 6.6 on another boom, took the ST104 and guess what: it was perfect day. Still F4 but steady 15 knots, a completely different kit and much more fun

F5: 101/6.7, a bit underpowered but always on the plane and going like crazy in the gusts

Please note that for the poll F4 was not included. F4 conditions are a bit tricky because this is the minimum condition for heavier windsurfers to get planing but for the lighter windsurfers, they will be very nicely powered up in 6.6 - 7m

I merely want to point out once more that wind estimations, purely based on the visual, can be really deceptive. Yesterday, we had unbelievable wind variations, because of SW wind combined with a lot of showers. When I arrived at my spot, my first impression was 6Bft. Yes, there were gusts up to 25 knots, deluding the water state with magical white caps. But these were merely gusts. 80% of the time or more, the average was only 15 knots, sometimes dropping to hardly 12 knots.
I've seen a lot of guys shlogging in the lulls with too small sails 5.xm2.